The invention relates to a method and apparatus for generating a signal representing uterine activity, and particularly to a monitor for obtaining and processing a uterine electromyography signal to produce a signal representative of uterine activity.
Uterine activity and fetal heart rate are two primary parameters measured in fetal monitoring during birth delivery. Current practice uses two methods to measure uterine activity. The first method is internal to the patient and uses an intrauterine pressure sensor (hereinafter referred to as a xe2x80x9cIUPxe2x80x9d sensor). The IUP sensor is an invasive device that can only be used after rupturing membranes. The IUP sensor produces an output that is a true function of uterine pressure and monitors contraction frequency and contraction duration. The second method is external to the patient and uses a tocodynamometer (hereinafter referred to as xe2x80x9ctocoxe2x80x9d). The toco is a non-invasive device that is placed on the maternal abdomen and is secured with an elastic belt or strap. The toco does not provide any information representative of uterine pressure, and is used to monitor contraction frequency and contraction duration. The output from the IUP sensor or the toco is processed by the fetal monitor and is printed or displayed on a uterine activity chart. An example uterine activity chart is shown in FIG. 1 where the uterine activity chart 10 displays a uterine activity waveform 15 resulting from a processed toco signal.
Uterine contractions are the result of coordinated contractions by individual myometrial cells of the uterus. At the cellular level, the contractions are triggered by an action potential. The action potential is a voltage signal that can be measured as an electromyography (hereinafter referred to as xe2x80x9cEMGxe2x80x9d) signal. During pregnancy, cellular electrical connectivity increases such that the action potential propagates to produce a coordinated contraction involving the entire uterus. The action potential during a uterine contraction can be measured with electrodes placed on the maternal abdomen resulting in a uterine EMG signal. The EMG signal is then processed to produce a signal that is functionally equivalent to a uterine activity signal created by a toco. The equivalent uterine activity signal provides contraction frequency and contraction duration information. In addition, the EMG signal approximates at least one component that would be acquired by an IUP sensor.
Accordingly, the invention provides a monitor. The monitor includes a sensor for acquiring a uterine EMG signal and a signal processor for generating a signal representative of uterine activity in response to the uterine EMG signal. The signal representative of uterine activity indicates uterine contraction frequency and contraction duration information. Additionally, the signal representative of uterine activity approximates a signal that would be acquired using either a toco or approximates at least one component of a signal that would be acquired using an IUP sensor.
In a first embodiment, the signal processor includes a receiver that receives the uterine EMG signal from the sensor and generates an analog signal representative of uterine activity. The signal processor further includes a microprocessor electrically connected to the receiver for receiving the analog signal representative of uterine activity and converting the analog signal representative of uterine activity into a digital signal representative of uterine activity. The signal processor also includes a memory unit electrically connected to the microprocessor for storing the digital signal representative of uterine activity.
In a second embodiment, the signal processor includes a microprocessor that receives the uterine EMG signal and generates a signal representative of uterine activity. The received uterine EMG signal can be a signal that is received directly from the sensor or can be a uterine EMG signal that has be processed by an amplifier and band-pass filter. The microprocessor includes software to perform digital signal processing techniques on the received uterine EMG signal.
The invention further provides a method of generating a signal representing uterine activity. The method includes the acts of obtaining a uterine EMG signal and processing the uterine EMG signal to produce a signal representative of uterine activity. In a first embodiment, the act of processing this uterine EMG signal includes the acts of amplifying the EMG signal, filtering the EMG signal, rectifying the EMG signal to obtain a rectified signal, applying the rectified signal to a peak detector to obtain an analog signal representative of uterine activity, sampling the analog signal representative of uterine activity to obtain data for a digital signal representative of uterine activity, and storing the data of the digital signal representative of uterine activity. In a second embodiment, the act of processing the uterine EMG signal includes the acts of sampling the uterine EMG signal to create a bipolar digital waveform, converting the bipolar digital waveform to a unipolar digital waveform, and time averaging the unipolar digital waveform to obtain the signal representative of uterine activity.
The invention further provides a system for generating a signal representing uterine activity. The system includes a sensor for obtaining a uterine electromyography (EMG) signal, and means for processing the uterine EMG signal to produce a signal representative of uterine activity.
The invention further provides a software program for operating a monitor. The monitor includes a sensor for acquiring a uterine electromyography (EMG) signal and a microprocessor for executing the software program. The software program operates the monitor by sampling the uterine EMG signal to obtain a bipolar digital waveform, and processing the sample uterine EMG signal to produce a signal representative of uterine activity.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.